Two good places to start looking are:
-Clean and soap-free glassware and brewing equipment. Avoid rinsing aids if you use a dishwasher.
-Fermentation temperatures. Warm fermentation, say 70F or above, maybe, produce more fusel alcohols that can be head killers.

70-75F is a good temperature for carbonating bottles, but it would be getting warm for a clean primary fermentation. Also, if you're storing the beer for very long, it's best to store the bottles as cold as possible once they're carbonated. I don't think that storing them warm would affect head retention, but they will stale faster. A month or so shouldn't matter.

Regarding head retention - You should have a set of glasses dedicated for beer use only. Other beverages can sometimes leave residues that are hard to remove. Use a detergent, not soap, to clean your glasses. I like TSP substitute. It gets my glasses clean without leaving any residue and it's cheap.

My beers are rarely fully carbonated in 1 week. Often they're ready in 2 weeks (plus a couple more days in the fridge for the CO2 to fully dissolve), but sometimes they take 3 or 4 weeks. One stout I made took 2 months for some reason.